This invention relates to a constant speed running device for vehicles to automatically adjust a vehicle speed to a set value.
In a conventional constant speed running device for vehicles to automatically control the opening degree of a throttle so as to adjust a vehicle speed to a set value (a stored speed), there is provided such a system as to increase or decrease the vehicle speed without using a throttle pedal. The system is operated by turning on a hand switch, so-called an accelerator switch (or a coast switch), and during the operating period of the accelerator switch the vehicle speed is increased (or decreased) asymptotically regardless of the set value, and the set speed value stored in a memory is renewed to a latest value at the same time.
FIG. 2 shows a timing chart where a present vehicle speed V.sub.1 is asymptotically increased during the operation of the accelerator switch. In the figure, a vehicle speed V.sub.2 at the time of turning off the accelerator switch is stored as a set speed in a memory. Thereafter, a feed back control is performed to set the speed V.sub.2 as an aimed value. In this case, the vehicle speed overshoots up to the speed value V.sub.3 due to a mechanical inertia. FIG. 3 shows a timing chart where a present vehicle speed V.sub.4 is asymptotically decreased. A vehicle speed overshoots a speed value V.sub.5 at the time of turning off the coast switch up to the low speed value V.sub.6 due to a mechanical inertia.
As described above, the conventional device can not stop the change of the vehicle speed immediately after turning off the accelerator switch or the coast switch. Therefore, the vehicle speed is adjusted to the stored value after the occurrence of the overshooting. Accordingly, there is such a problem as to give uncomfortable feeling and shock to a driver.